The present disclosure relates to methods and devices for replacing heart valves.
Patients with defective aortic heart valves are often candidates for a replacement heart valve procedure. The conventional treatment is the surgical replacement of the heart valve with a prosthetic valve. This surgery involves a gross thorocotomy or median sternotomy, cardiopulmonary bypass and cardiac arrest, surgical access and excision of the diseased heart valve, and replacement of the heart valve with a prosthetic mechanical or tissue valve. Valves implanted in this manner have historically provided good long term outcomes for these patients, with durability of up to ten or fifteen years for tissue valves, and even longer for mechanical valves. However, heart valve replacement surgery is highly invasive, can require lengthy recovery time, and is associated with short and long term complications. For high surgical risk or inoperable patients, this procedure may not be an option.
Recently, a minimally invasive approach to heart valve replacement has been developed. This approach, known as transcatheter aortic valve implantation (TAVI), relies on the development of a collapsible prosthetic valve which is mounted onto a catheter-based delivery system. This type of prosthesis can be inserted into the patient through a relatively small incision or vascular access site, and may be implanted on the beating heart without cardiac arrest. The advantages of this approach include less surgical trauma, faster recovery time, and lower complication rates. For high surgical risk or inoperable patients, this approach offers a good alternative to conventional surgery. Examples of this technology are the Sapien Transcatheter Valve (Edwards Lifesciences, Irvine, Calif.) and the CoreValve System (Medtronic, Minneapolis, Minn.). U.S. Pat. No. 6,454,799, which is incorporated herein by reference in its entirety, describes examples of this technology.
There are two main pathways for valves inserted using the TAVI approach. The first is a vascular approach via the femoral artery (referred to as a transfemoral approach), either percutaneously or through a surgical cut-down and arteriotomy of the femoral artery. Once placed into the femoral artery, the valve mounted on the delivery system is advanced in a retrograde manner up the descending aorta, around the aortic arch, and across the ascending aorta in order to be positioned across the native aortic valve. Transfemoral aortic valve delivery systems are typically over 90 cm in length and require the ability to navigate around the aortic arch. The relatively small diameter of the femoral artery and the frequent presence of atherosclerotic disease in the iliofemoral anatomy limits the maximum diameter of the delivery system to about 24 French (0.312″) in diameter. The second pathway, termed transapical, involves accessing the left ventricle through the apex of the heart via a mini-thorocotomy, and advancing the valve delivery system in an antegrade fashion (in the same direction as blood flow) to the aortic valve position. This pathway is much shorter and straighter than the transfemoral path, but involves a surgical puncture and subsequent closure of the wall of the heart.
Other approaches have been described, including access from the subclavian artery, and direct puncture of the ascending aorta via a mini-thorocotomy. The subclavian approach (transsubclavian approach) has been used when the transfemoral route is contra-indicated, but may block flow to the cerebral vessel through the ipsilateral common carotid artery. A direct aortic puncture is usually considered if all other routes must be excluded due to anatomic difficulties including vascular disease. Puncture of the aortic wall, and subsequent closure, carries associated surgical risk including aortic dissection and rupture.
The transfemoral approach to the aortic valve, as opposed to the transapical approach, is a generally more familiar one to the medical community. Accessing the ascending aorta from the femoral artery is standard procedure for interventional cardiologists. Balloon valvuloplasty procedures via the transfemoral approach have been performed for years. The surgical approaches such as the transapical access or direct aortic puncture are less familiar and require practitioners with both surgical and endovascular skills; techniques for the surgical approaches are still evolving and whether they offer advantages over the transfemoral and transsubclavian methods have yet to be determined. However, problems also exist with the transfemoral and transsubclavian approaches. One is that the desired access vessel is often too small and/or is burdened with atherosclerotic disease, which precludes the artery as an access point. A second problem is that the pathway from the access point to the aortic valve usually involves one or more major turns of at least 90° with a relatively tight radii of curvature, 0.5″ or less, requiring a certain degree of flexibility in the delivery system. This flexibility requirement restricts the design parameters of both the valve and the delivery system, and together with the required length of the delivery system reduces the level of control in accurately positioning the valve.
Both the transfemoral and transapical approaches have as potential complications the dislodgement of atherosclerotic and/or thrombotic debris, so-called “embolization” or the creation of “embolic debris,” during both access maneuvers and implantation of the prosthetic valve. The most serious consequence of embolic debris is that it travels with the blood flow to the brain via one or more of the four primary conduits to the cerebral circulation, namely the right and left carotid arteries and the right and left vertebral arteries. Transfemoral TAVI procedures require passage of large device and delivery system components through the aortic arch and across the origins of the head and neck vessels that supply blood flow to the carotid and vertebral arteries, potentially loosening, fragmenting, and dislodging debris during its route to the aortic valve. The transapical TAVI procedure involves a puncture of the heart wall, which may generate embolic debris from the wall of the ventricle or ascending aorta, or may form thrombus or clot at the apical puncture location. During the vigourous motion of the beating heart, this clot can break free and travel to the brain as well. Both approaches require significant manipulation while the prosthetic valve is being placed: the TAVI implant and delivery system moves back and forth across the native aortic valve, potentially dislodging more debris from the diseased valve itself. With expansion of the valve implant, the native aortic valve is compressed and moved out of the stream of the cardiac output, another moment when the shearing and tearing of the native valve can free more debris to embolize to the brain.
Recently, there has been described an embolic filter protection device for use with TAVI procedures, as referenced in U.S. Patent Application Publication No. 20080065145, which is incorporated herein by reference in its entirety. This device places a temporary screen over the ostium of the head and neck vessels to prevent passage of embolic particles while allowing blood flow into the vessels. While this device may offer some protection from larger embolic particles, it requires an additional vascular access and device deployment, adding to the cost and time of the procedure, and does not facilitate the passage of the prosthetic valve itself. Moreover, it does not provide protection during filter placement and retrieval; since the filter is deployed against the wall of the aorta, there is a high chance that the filter manipulation itself will be the cause of embolic complications.